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Date: Thu, 7 Oct 2010 21:55:56 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>, Minchan Kim <minchan.kim@...il.com>, Greg Thelen <gthelen@...gle.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>, Balbir Singh <balbir@...ux.vnet.ibm.com> Subject: Re: [PATCH v2] memcg: reduce lock time at move charge (Was Re: [PATCH 04/10] memcg: disable local interrupts in lock_page_cgroup() On Fri, 8 Oct 2010 13:37:12 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote: > On Thu, 7 Oct 2010 16:14:54 -0700 > Andrew Morton <akpm@...ux-foundation.org> wrote: > > > On Thu, 7 Oct 2010 17:04:05 +0900 > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote: > > > > > Now, at task migration among cgroup, memory cgroup scans page table and moving > > > account if flags are properly set. > > > > > > The core code, mem_cgroup_move_charge_pte_range() does > > > > > > pte_offset_map_lock(); > > > for all ptes in a page table: > > > 1. look into page table, find_and_get a page > > > 2. remove it from LRU. > > > 3. move charge. > > > 4. putback to LRU. put_page() > > > pte_offset_map_unlock(); > > > > > > for pte entries on a 3rd level? page table. > > > > > > This pte_offset_map_lock seems a bit long. This patch modifies a rountine as > > > > > > for 32 pages: pte_offset_map_lock() > > > find_and_get a page > > > record it > > > pte_offset_map_unlock() > > > for all recorded pages > > > isolate it from LRU. > > > move charge > > > putback to LRU > > > for all recorded pages > > > put_page() > > > > The patch makes the code larger, more complex and slower! > > > > Slower ? Sure. It walks the same data three times, potentially causing thrashing in the L1 cache. It takes and releases locks at a higher frequency. It increases the text size. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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